The objectives of the research proposed in this application are the study of specific aspects of the control of collagenase expression by progesterone and other hormones in the post-partum uterus, in vivo and in vitro. Collagenase is required for the initiation of collagen degradation in the uterus, and thus its regulation is of critical importance in the maintenance of the uterus in normal reproductive states. Progesterone selectively inhibits the expression of collagenase in the uterus. The effect of progesterone, and other hormones of reproductive significance in an in vitro tissue culture system of post- partum uterus will be investigated. These studies should provide fundamental information regarding an important function of progesterone in the mammalian uterus. In addition, information obtained from the investigation should provide valuable approaches to the study of mechanisms of regulation of collagen in a variety of other connective tissues.